The Arch of Constantine is a triumphal arch in Rome, situated between the Colosseum and the Palatine Hill. It was erected to commemorate Constantine's victory over Maxentius at the Battle of Milvian Bridge on October 28, 312 AD. Dedicated in 315 AD, it is the latest of the extant triumphal arches in Rome, from which it differs by spolia, the extensive re-use of parts of earlier buildings.

General descriptionThe arch is 21 m high, 25.7 m wide and 7.4 m deep. It has three archways, the central one being 11.5 m high and 6.5 m wide, the lateral archways 7.4 m by 3.4 m each. The lower part of the monument is built of marble blocks, the top (called attic) is brickwork revetted with marble. A staircase formed in the thickness of the arch is entered from a door at some height from the ground, in the end towards the Palatine Hill. The general design with a main part structured by detached columns and an attic with the main inscription above is modelled after the example of the Arch of Septimius Severus on the Forum Romanum. It has been suggested that the lower part of the arch is re-used from an older monument, probably from the times of the emperor Hadrian (Conforto et al., 2001; for a defence of the view that the whole arch was constructed in the 4th century, see Pensabene & Panella). The arch spans the Via Triumphalis, the way taken by the emperors when they entered the city in triumph. This route started at the Campus Martius, led through the Circus Maximus and around the Palatine Hill; immediately after the Arch of Constantine, the procession would turn left at the Meta Sudans and march along the Via Sacra to the Forum Romanum and on to the Capitoline Hill, passing both the Arches of Titus and Septimius Severus. During the Middle Ages, the Arch of Constantine was incorporated into one of the family strongholds of ancient Rome. Works of restoration were first carried out in the 18th century; the last excavations have taken place in the late 1990s, just before the Great Jubilee of 2000.

DecorationThe decoration of the arch heavily uses parts of older monuments, which are given a new meaning in the context of the Constantinian building. As it celebrates the victory of Constantine, the new "historic" friezes illustrating his campaign in Italy convey the central meaning: the praise of the emperor, both in battle and in his civilian duties. The other imagery supports this purpose: decoration taken from the "golden times" of the Empire under Trajan, Hadrian and Marcus Aurelius places Constantine next to these "good emperors", and the content of the pieces evokes images of the victorious and pious ruler. Another explanation given for the re-use is the short time between the start of construction (late 312 at the earliest) and the dedication (summer 315), so the architects used existing artwork to make up for the lack of time to create new art. As yet another possible reason, it has often been suggested that the Romans of the 4th century lacked the artistic skill to produce acceptable artwork and therefore plundered the ancient buildings to adorn their contemporary monuments. This interpretation has become less prominent in more recent times, as the art of Late Antiquity has been appreciated in its own right. It is, of course, possible that a combination of two or all three of those explanations are correct, as they are not mutually exclusive.

AtticAbove the middle archway, the main inscription (see below) takes the most prominent place of the attic. It is identical on both sides of the arch. Flanking the inscription on both sides, there are pairs of relief panels above the minor archways, 8 in total. They were taken from an unknown monument erected in honour of Marcus Aurelius, and show (north side, left to right) the emperor's return to Rome after the campaign (adventus), the emperor leaving the city and saluted by a personification of the Via Flaminia, the emperor distributing money among the people (largitio), the emperor interrogating a German prisoner, (south side, left to right) a captured enemy chieftain led before the emperor, a similar scene with other prisoners, the emperor speaking to the troops (adlocutio), and the emperor sacrificing pig, sheep and bull. Together with three panels now in the Capitoline Museum, the reliefs were probably taken from a triumphal monument commemorating Marcus Aurelius' war against the Sarmatians from 169 – 175, which ended with his triumphant return in 176. On the largitio panel, the figure of Marcus Aurelius' son Commodus has been eradicated after the latter's damnatio memoriae. On top of each of the columns stand marble statues of Dacian prisoners from the times of Trajan, probably taken from the Forum of Trajan. From the same time date the two large (3 m high) panels decorating the attic on the small sides of the arch, showing scenes from the emperor's Dacian Wars. Together with the two reliefs on the inside of the central archway, they came from a large frieze celebrating the Dacian victory. The original place of this frieze was either the Forum of Trajan, as well, or the barracks of the emperor's horse guard on the Caelius.

Main sectionThe general layout of the main facade is identical on both sides of the arch. It is divided by four columns of Corinthian order made of Numidian yellow marble (giallo antico), one of which has been transferred into the Basilica di San Giovanni in Laterano and was replaced by a white marble column. The columns stand on bases showing victory figures on front, and captured barbarians and Roman soldiers on the sides. The spandrels of the main archway are decorated with reliefs depicting victory figures with trophies, those of the smaller archways show river gods. Column bases and spandrel reliefs are from the times of Constantine. Above each lateral archway are pairs of round reliefs dated to the times of emperor Hadrian. They display scenes of hunting and sacrificing: (north side, left to right) hunt of a boar, sacrifice to Apollo, hunt of a lion, sacrifice to Hercules, (south side, left to right) departure for the hunt, sacrifice to Silvanus, hunt of a bear, sacrifice to Diana. The head of the emperor (originally Hadrian) has been reworked in all medaillons: on the north side, into Constantine in the hunting scenes and into Licinius or Constantius I in the sacrifice scenes; on the south side, vice versa. The reliefs, c. 2 m in diameter, were framed in porphyry; this framing is only extant on the right side of the northern facade. Similar medaillons, this time of Constantinian origin, are placed on the small sides of the arch; on the eastern side, showing the Sun rising, and on the western side, the Moon, both on chariots. The main piece from the time of Constantine is the "historical" relief frieze running around the monument under the round panels, one strip above each lateral archway and at the small sides of the arch. These reliefs depict scenes from the Italian campaign of Constantine against Maxentius which was the reason for the construction of the monument. The frieze starts at the western side with the "Departure from Milan". It continues on the southern, "outward" looking face, with the siege of a city, probably Verona, which was of great importance to the war in Northern Italy; also on that face, the Battle of Milvian Bridge with Constantine's army victorious and the enemy drowning in the river Tiber. On the eastern side, Constantine and his army enter Rome; the artist seems to have avoided using imagery of the triumph, as Constantine probably did not want to be shown triumphant over the Eternal City. On the northern face, looking "towards" the city, two strips with the emperor's actions after taking possession of Rome: Constantine speaking to the citizens on the Forum Romanum, and distributing money to the people.

Inner sides of the archwaysIn the central archway, there is one large panel of Trajan's Dacian War on each wall. Inside the lateral archways are eight portraits busts (two on each wall), destroyed to such an extent that it is no longer possible to identify them.

InscriptionsThe main inscription would originally have been of bronze letters. It can still be read easily, though only the recesses in which the letters sat, and their attachment holes, remain. It reads thus, identically on both sides:

To the Emperor Caesar Flavius Constantinus, the greatest, pious, and blessed Augustus: because he, inspired by the divine, and by the greatness of his mind, has delivered the state from the tyrant and all of his followers at the same time, with his army and just force of arms, the Senate and People of Rome have dedicated this arch, decorated with triumphs.

The words instinctu divinitatis ("inspired by the divine") have been much commented. They are usually read as sign of Constantine's shifting religious affiliation: The Christian tradition, most notably Lactantius and Eusebius of Caesarea, relate the story of a vision of the Christian god to Constantine during the campaign, and that he was victorious in the sign of the cross at the Milvian Bridge. The official documents (esp. coins) still prominently display the Sun God until 324 AD, while Constantine started to support the Christian church from 312 on. In this situation, the vague wording of the inscription can be seen as the attempt to please all possible readers, being deliberately ambiguous, and acceptable to both pagans and Christians. As was customary, the vanquished enemy is not mentioned by name, but only referred to as "the tyrant", drawing on the notion of the rightful killing of a tyrannical ruler; together with the image of the "just war", it serves as justification of Constantine's civil war against his co-emperor Maxentius.

Two short inscriptions on the inside of the central archway transport a similar message: Constantine came not as conqueror, but freed Rome from occupation:

They give a hint on the date of the arch: "Solemn vows for the 10th anniversary – for the 20th anniversary" and "as for the 10th, so for the 20th anniversary". Both refer to Constantine's decennalia, i.e. the 10th anniversary of his reign (counted from 306), which he celebrated in Rome in the summer of 315 AD. It can be assumed that the arch honouring his victory was inaugurated during his stay in the city.